Receptacle and method of making the same



March 25, 1952 s. s. STEVENS 2,590,221

RECEPTACLE AND METHOD OF MAKING THE SAME Filed April 25, 1947 5Sheets-Sheet l INVENTOR SH/ IUEL 5. STEVENS ATTORNEY March 25, 1952 s.s. STEVENS 2,590,221

RECEPTACLE AND METHOD OF MAKING THE SAME Filed April 25, 1947 5Sheets-Sheetfl INVENTOR mvzuEL S. 5 TEVE/VS TT RNEY March 25, 1952 sQs.STEVENS 2,590,221

RECEPTACLE AND METHOD OF MAKING THE SAME Filed April 25. 1947 3Sheets-Sheet 3 F5 LU INV TOR SHMUEL 5 TEVENS Ma -g,

A ORNEY Patented Mar. 25, 1952 RECEPTACLE AND'METHOD OF MAKING THE SAMESamuel S. Stevens, Plattsburg, N. Y., assignor, by mesne assignments, toThe Diamond Match Company, New York, N. Y., a corporation of DelawareApplication April 25, 1947, Serial No. 743,857

10 Claims.

This invention relates to molded fibre articles having an interior lineror exterior covering, or both, of an organic plastic to render the wallof the article impervious to vapors and liquids. The invention isdirected to the product and to the method of making the same.

Without limiting the invention to an article for any specific use,reference may be made, for the purpose of illustration, to theemployment of this invention in connection with molded fibre receptaclessuitable for packaging frozen food products. For the successful andeffective packaging of such products, it is necessary to have a sturdypackage which will withstand machine handling incident to filling,packaging and sealing of the food product and one which will withstandrough handling in storage and delivery to the ultimate consumer.

It is also necessary that such a receptacle retain all of theconstituents of its contents and prevent the ingress or egress of fluidor vapors which would contaminate the product if coming from the outsideand would permit the loss of essential ingredients of the product ifallowed to escape from the inside. For example, it is both desirable andnecessary to retain within the package the water or moisture content ofthe product throughout the time when it is stored, so that when itreaches the consumer, it will be in exactly the same state and conditionwhen it was packed.

In food packages of the type heretofore used for the packaging of frozenfoods, it has been customary to form the package from fiat sheet stockor board by either or both cutting and folding it into receptacle form.If the sheet of material thus used is surface pretreated by ordinarycoating methods, prior to forming it into the receptacle, the formingoperation tends to break or weaken the coating along the fold lines orcreases, with the result that leakage or contamination of the productmay result. Furthermore, the folds or creases are difficult tovefiectually seal against the passage of vapor and generally produceleakage areas with the result that theproduct may deteriorate or becomecontaminated.

In contradistinction to the conventional prior practice, the containerof the present invention is molded and dried in its ultimate shapewithout creases, folds or score lines of any kind in its surface, sothat its wall may be of substantially uniform thickness throughout andconsequently of maximum strength and rigidity for the stock employed.This container may be conveniently produced by suction molding it eitherfrom wood pulp or other fibres, on a forming die to the desired shapeand thereafter drying the resulting article between hot drying dieswhile under pressure between said dies to produce a relatively smoothsurfaced article of fine texture and pleasing appearance. The containerwhich results from these operations preferably con- 1sjtitutes the bodyof the receptacle of this inven- 1011.

In carrying out the present invention, I start with a molded containerbody of this character. Over the interior or exterior of such body isthen laminated a relativel thin sheet of an or ganic plastic which isadhered to said body at all points where it comes in facial contacttherewith. The preferred method of adhering the sheet to the body, isbased upon, certain discoveries which I have made, to wit: if arelatively thin sheet of an organic thermoplastic is placed against afibrous surface which is heated to a temperature sufiicient to renderthe plastic fiowable or tacky while the opposite surface of such sheetis maintained at a temperature below the softening point of the plasticand pressure is applied to the sheet, the thus heated surface strata ofthe sheet will become fused and tend to flow into the interstices of thecontacting fibrous surface with the result that, when the fibrousarticle is subsequently cooled, that portion of the plastic which hasentered into its structure will harden therein and form therewith apermanent bond between the fibrous material and the plastic sheet.

An important requirement of this procedure consists in maintaining atleast a portion of the thickness of the plastic sheet, remote from thefibrous body, in solid unfused condition throughout the entire operationfor it has been found that, if the heat of such body penetrates entirelythrough the plastic sheet so as to fuse it for its entire thickness, thecontiguity of the sheet will be destroyed, pin holes willresult and thesheet will not produce an impervious, seal over the fibrous body towhich it is applied. Therefore, in the preferred manner of'practicingthe present invention, the dies or other expedients, through theutilization of which the organic sheet is applied to the fibroussurface, are preferably cooled by water or air circulation or otherwiseto maintain that strata of the organic sheet which engages therewith inits normal-solidified and unfused condition throughout. v

In compositing the body of the receptacl l and its lining or coveringsheet, the body of the receptacle is preferably heated by an appropriatedie or dies, shaped to conform with the body, so as to raise thetemperature of such body to the desired degree. The liner or coveringsheet is preferabl formed or shaped to conform with the surface of thebody to which it is to be attached on a complementary die which ispreferably provided with means for maintaining said die cool. After thecontainer body is heated and the plastic layer has been formed asstated, they are brought together, preferably on substantiallyconforming complementary dies, to effect surface contact between thecontainer body and the plastic sheet and they are thereupon held in suchcontact until the surface strata of the sheet which is in engagementwith the body shall have been softened or fused sumciently to provide aneffective bond while the remainder of the thickness of the sheet is keptbelow its fusion point. After fusion, with or without penetration, hasoccurred, the entire article is cooled to complete the assembly.

Features of the invention, other than those specified, will be apparentfrom the following detailed description and appended claims when read inconjunction with the accompanying drawings, wherein:

Figure 1 shows the cross section through an illustrative type of moldedfibre article to which the liner covering sheet is to be applied. Thisarticle may be round, rectangular, square, or of any desirable shape.

Figure 2 shows a piece of flat sheet stock to be applied to the articleof Figure 1.

Figure 3 shows the finished article in cross section with the sheetapplied thereto as a liner.

Figure 4 shows the cross section of a heated die with the article ofFigure 1 thereon.

Figure 5 shows the fibre article being held between two heated dies toinsure that the article is properly preheated, the outer die, or the dieon the bottom of the article, preventing the escape of heat applied bythe die heating the inner surface of the article.

Figure 6 shows the die on which the liner sheet is preformed. As shown,the sheet has been laid on the fiat surface of the die and is held thereby suction or vacuum applied through the openings in this flat surface.

tion of the sheet may be cut out at the corners to facilitate its beingshaped over the die of Figure 6.

Figure 8 shows, the surplus material at the periphery of the sheet beingremoved, leaving the sheet of just the size to overlie and cover theinner surface of the article and the upper edge of the latter.

Figure 9 shows a transfer die for removing the article from the die ofFigure 4. This is preferably a suction or vacuum die.

Figure 10 shows the article held between the transfer die of Figure 9and the sheet applying die of Figure 6. After removal from between thetwo dies shown in Figure 10, the receptacle will be in the finished formshown in Figure 3.

According to this invention the plastic sheet may be made to covereither or both the inner and outer surfaces of the container body.However, for the purpose of concrete illustration I will hereinafterdescribe the mode of applying such sheet to the inside and uppersurfaces of the container body so that it will serve as a linertherefor. It should be noted, however, that the same procedure may beutilized in applying said sheet to the exterior surfaces of such body.

The sheet material preferably used for this purpose in accordance withthis invention is in the nature of an organic plastic havingthermoplastic properties and while many such synthetic plastics may beemployed, the following may be referred to as illustrative, viz:

Cellulose acetate Cellulose acetate butyrate Chlorinated rubber LatexPolyethylene (Polythene) Vinvyl acetal Vinyl acetate Vinyl alcohol Vinylcarbozole Vinyl chloride-vinylidene chloride Rubber hydrochloride(Pliofilm) Cellophane (regenerated cellulose) Vinyl chloride Vinylchloride-acetate Vinylidene chloride Ethyl cellulose Sodiumcarboxymethyl cellulose Polyvinyl alcohol Polyvinyl chloride To beefiicient, inexpensive, and readily applicable to the body, this sheet,which is indicated in the drawings by the reference character S, shouldbe quite thin. The drawings show the sheet relatively thick for thepurpose of illustration, but, in practice, a ver thin sheet ispreferably employed.

The container body illustrated in Figure l and indicated by thereference character B is of molded fibre, as hereinbefore indicated, andit is of finished shape without folds or creases.

It is desirable to use a sheet S of minimum thickness, and, accordingly,I preferably employ a container body B of the kind which is suctionmolded from a liquid-fibre mixture, e. g., paper pulp, and subsequentlydie-dried by pressing a heated die against at least the surface of thebody to which the sheet S is to be applied. This produces on the moldedand die-dried article a smooth even surface well adapted to contactthroughout with a thin sheet of plastic material also having a smootheven surface.

To effectually unite the sheet S of Figure 2 and the container body B ofFigure 1 according to this invention to form a unitary structure whereinthe parts are substantially permanently adhered to one another, it isnecessary to bring the surface of the body to which the liner sheet S isto be applied to a temperature sufiiciently high to fuse or soften suchsheet but not so high as to disintegrate it throughout its thicknesswhen manipulated as hereinafter described. The heating of the body maybe accomplished as a part of the method of making the body. However,this heating may be accomplished by utilizing the die I shown in Figure4, which is illustrated in this figure as provided with heating channels2 through which a heating fluid may be circulated or in which anelectrical heating element may be positioned for this purpose. Throughthe employment of such appropriate heating means, the die I may bebrought to and maintained at an optimum temperature which terior, twochambers 6 and l.

:will manifestly dependupon the particular thermoplastic of whichthe-sheet S is: constituted. To assist 'in theheating of theinnersurface of thebody B andto' protect the outer surface an'dpreventheat froinbeing radiated therefrom, I provided a second die 3, shown inFigure 5, whichzserves to press the inner surface of the article againstdie I and hold it in firm contact therewith; Die-3 may be heated byelectric heating elements t or by any other suitablemeans. Ll. socontrolthe temperatures of dies l and 3 Ithatthe inner surface of the articlewill be heated .tojust the proper temperature to facilitate theapplication of the sheet of thermoplastic. material and to insure aneven and uniform adhesion thereto.

To. pre-shape or pre-form the sheet of thermoplastic material, I providea die structure 5 shown in Figure 6. This die structure has, in item-From the chamber l, passages'or ducts 1a lead to the upper or flatsurface of the die while passages 6a lead from the chamber 6 to theexterior sides of the die so that partial vacuum or suction may becommunicated to these exterior surfaces. Vacuum or suction connection tochamber '6 is provided overhang the sides of the die. Suction may becommunicated; to the chamber 1 to holdthesheet in place on the die whilethe overhanging or pro.- .jecting portions of the sheet are folded downover the sides of the die successively, the surplus material being'takenup by a series of pleats or folds so that the sheet is caused to closelyconform to the die 5 as shown in Figure 7. This conforming of the sheetto the die may be accomplished manually or by. any appropriate foldingor forming means but in any event suction communicated to the chambers 6and 1 either before, during or after the forming operation will hold thesheet in this conformity upon the completion thereof.

In practice thesheet S may be preliminarily cut to a contour of theexact shape and size necessary to exactly cover the interior surfaceandrupper edges of the body B soasto eliminate thenecessity forsubsequent trimming but in practiceI prefer to form this sheet welloversize andto trim it after it has been formed, as shown in Figure 7,by trimming knives II], as illustrated in Figure 8, which trim from themargins the excess-ll.

In Figure 6 it will be noted that the die 5 is mounted upon a member I!which is in effect -a-coo1ing plate, provided therein with passagesj,l3;th10ugh which a cooling medium may be circulated to cool the die 5and thus keep the surface strata of the sheet contiguous therewith atall times below its fusion or disintegrating point by drawing off enoughheat from that face of the sheet to accomplish this result. Bycontrolling the temperature of the water or other medium which iscirculated through the passages l3, the temperature of the die surfacewhich" engages thesheet maybe accurately regulated and maintained atsuch degree as to pre- 'clude fusionthereof and-maintainits contiguity.

In practice it, is found'convenient toprepare the 6sheets-forapplicationto thebody B=while the latter is being heated.

- Afterthe plastic sheet has been formed as shown in Figure "'7 andtrimmed as shown in Figure '8 and the. container body has been heated tothe desired temperature, these parts are laminated. This may beconveniently accomplished -by:means of a combined transfer and applyingdie M, such as shown in Figure 9. The die 14 is chamberedas shown at 15and suction may be communicated to this chamber through a pipe I6 andmade effective upon the inner surfaceof the die through suctionpassages. The die 14 is backediup by a plate l8 having thereinpassages).- so that: the-temperature of the die l4 may 'be'controlled.Either a heating or a; cooling fluidimay be circulated throughthepassages I9 as may be desired at different stages of the method.

The die I4, when utilized as a transfer die, is brought intocontact'with the exterior face of the hot body B after the die 3 ofFigure 5 has been removed therefrom and'while thebody remains on the hotdie I, sothat the. parts appear as shownin Figure 9. Suction is appliedto the chamber 1 5 and causes the article to be gripped by the'die-M'sothat said die l4 may be moved relative to the-die l'to remove the body Bfrom said die and transfer said'body into the position shown inFigure-10 wherein it is contacted with the formed sheet on the die 5.This operation is carried on expeditiously so that the interior surfaceof the container body willnot appreciably cooland,-'if*desired, thedieI4 may be a heated die at this time to-keep the'bodyhot.

When the relatively cool sheet S is brought into contact with thesurface of the-hot body B, and theyare'pre'ssed together by thecooperating dies 5 and M, as shown in Figure 10, the heat of thecontacting surface of the hot body-fuses or softens the contiguousstrata of'the' plastic layer. In some cases, the fusion of the sheet maybe carried only to" such a point as to produce a sufficiently tackycondition of the plastic to effect adherence of the sheet to the bodywhen both are restored to room temperature. In other cases, the fusionof the thermoplasticmaterial may be carried so far as to cause the fusedand softened plastic to flow into surface conformity with the body andenter to some extent into the interstices of the fibrous structurethereof.

The latter'procedure may be very efficiently carried out if thecontainer body B is of the smooth die-dried variety, for the surface ofsuch an'articl'e is so smooth and even as to contact with practicallyall portions of the smooth and even surface of the plastic sheet and itthus requires very little flow of the plastic to effect the penetrating,interlocking bond which thus occurs. Even with this type of finishmerely a tacky condition may be availed of to form the bond if desired.However, in adhering the'sheet to some of the rougher types of containerbody, the tacky condition is recommended and it-is not'recommended'thatany attempt be made to appreciably flow a portion of the thickness of arelatively thin sheet into conformity with a rough, uneven surface,although it may be done with a thicker sheet.

It should be-noted that, during the fusion of that portion of theplastic sheet which contacts with the hotbody, the opposite surfacestrata of the sheet is kept below its fusion point by the cooling effectof the relatively cool die 5 with which it contacts, but this coolingeffect of the article and from between the parts.

die is localized at this surface of the sheet and does not preclude theamalgamation of the folds which were formed in the sheet during theforming step shown in Figure '7. In fact, if the material is permittedto fiow considerably the contacting portions of the material in thesefolds will fuse together and become substantially homogeneous. Even whenonly the tacky condition, hereinbefore referred to, is produced, thefolds will be sufliciently heated to heat-seal themselves; so that theywill not thereafter tend to open or separate.

I have referred to pressure between the dies and M as utilized to pressthe sheet and container body into intimate relation with one another. Ifdesired, these dies may be provided with some clearance between theircoacting faces and merely make a firm seal around the edges of thearticle, so as to permit compressed air, at a temperature below thefusion point of the plasticjto enter into the chamber 1 through pipe 9,circulate through passages la to the outer surface of the die 5 andalong the outer surface of such die to passages 6a, and through saidpassages to the chamber 6, to exit through the pipe 8. If compressed airis thus admitted, the sheet will be forced firmly against the hotcontacting surface of the body B and contact throughout these parts maythereby be assured.

The use of compressed air in the manner stated may be availed of inapplying the thermoplastic sheet to either rough or smooth finishedcontainer bodies and, irrespective of the thickness of the sheet, but itis particularly eflicient in applying relatively thin sheets to otherthan smooth die-dried surfaces.

It is also feasible to apply thicker sheets to the rougher surfacedarticles wholly by die pressur'e and without the use of compressed airas stated, but, when this is done, the sheets should be sufficientlythick to permit substantially allover surface contact during the fusingstep with concurrent effective maintenance of the opposite surfacestrataof the sheet below its fusion temperature.

When the sheet S and the body B are superimposed, air is apt to betrapped therebetween and unless this air is removed, proper bonding ispractically impossible. For this reason suction should be maintainedwithin the die l4, through the suction pipe l6, during the entirecompositing period, so as to draw such entrained air through the articlebody and thu evacuate it from the Moreover, this suction should bemaintained throughout the fusion period and it is preferably continueduntil this step is completed and the assembled body and sheet areremoved from the die l4.

After the fusion step has taken place, the die I4 may be immediatelyremoved leaving the composited finished receptacle on the die 5, fromwhich it may be removed by any suitable pick-off die or by hand, or, ifdesired, the dies 5 and is may be left in assembled relation while thecooling medium is circulated through the passages l9 to lower thetemperature of the entire assembly to a point whereat the thermoplasticwill solidify and set with the parts permanently bound together.Thereafter the die I4 may be utilized as a pick-off die to remove thefinished receptacle from the die 5 and transfer it to any appropriatedischarge station for packing or otherwise.

Experience with the method hereinbefore de-- scribed has demonstratedits efficacy in the production of a strong and. durable receptacleabsolutely impervious to the passage of vapor and moisture and welladapted for the hermetic sealing of the package which it forms. Anysuitable cover may be associated with this receptacle but it ispreferably in the form of a fiat layer of fibrous material correspondingto the body and having composited therewith a sheet of thermoplasticmaterial united thereto in the same manner as that employed incompositing the receptacle. Such cover may be secured in place in anyappropriate manner or by any desired means without departing from thiinvention, although I preferably heat-seal it in position on thereceptacle.

The foregoing detailed description sets forth the invention in itspreferred practical form, but the invention is to be understood as fullycommensurate with the appended claims.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

l. The method of compositing an imperforate fibrous receptacle body anda sheet of thermoplastic which comprises: heating an imperforate fibrousreceptacle body to a temperature above the fusion temperature of thethermoplastic sheet to be composited therewith, thereafter shaping andbringing such sheet of thermoplastic into facially contactingconformation with one face of said imperforate heated fibrous body, andholding them in contactfor a sufficient period of time to permit theheat of the body to fuse the surface strata of the contiguous side ofthe sheet into bonding condition while maintaining the opposite side ofthe sheet at a temperature below the fusion point of such thermoplastic,whereby the sheet and fibrous body become firmly adhered together bysolidification and setting of the resulting thermoplastic bond whensubsequently cooled.

2. The method of compositing an imperforate fibrous receptacle body anda sheet of thermoplastic which comprises: heating an imperforate fibrousreceptacle body to a temperature above the fusion temperature of athermoplastic sheet to be composited therewith, thereafter shaping andbringing such sheet of thermoplastic into facially contactingconformation with one face and the open edge of said imperforate heatedfibrous body, and holding them in contact for a sufiicient period oftime to permit the heat of the body to fuse the surface strata of thecontiguous side of the sheet into bonding condition while maintainingthe opposite side of the sheet at a temperature below the fusion pointof such thermoplastic, whereby the sheet and fibrous body become firmlyadhered together by solidification and setting of the resultingthermoplastic bond when subsequently cooled.

3. The method of compositing an imperforate fibrous receptacle body anda sheet of thermoplastic which comprises: forming a sheet ofthermoplastic into a shape to substantially conform to one surface ofthe fibrous receptacle body with which said sheet i to be composited,heating the fibrous receptacle body while free from contact with saidformed thermoplastic sheet to a temperature above the fusion temperatureof said thermoplastic sheet, thereafter bringing the formedthermoplastic sheet and the heated fibrous receptacle body intoconforming facial contact, and holding them in such contact for asufficient period of time to permit the heat of the receptacle body tofuse the surface strata of the contiguous side of the sheet into bondingcondition while maintaining the opposite side of the sheet at atemperature below the fusion temperature of the thermoplastic sheet,whereby the sheet and fibrous body become firmly adhered together bysolidification and setting of the resulting thermoplastic bond whensubsequently cooled.

4. The method of compositing an imperforate fibrous receptacle body anda sheet of thermoplastic which comprises: folding a flat thermoplasticsheet into a shape to conform with one surface of the fibrous receptaclebody with which said sheet is to be thereafter composited, heating thefibrous receptacle body while free from contact with said foldedthermoplastic sheetto a temperature above the fusion temperature of saidsheet, thereafter bringing the folded thermoplastic sheet and the heatedreceptacle bodyv into nesting relation with their contiguous faces incontact, and maintaining them in such contact for a sufficient period oftime to permit the heat of the receptacle body to fuse the surfacestrata of the contiguous sides of the sheet into bonding condition whilemaintaining the opposite sides of the sheet at a temperature below thefusion temperature of the thermoplastic sheet, whereby the sheet andfibrous body become firmly adhered together by solidification andsetting of the resulting thermoplastic bond when subsequently cooled.

5. The method of compositing an imperforate fibrous receptacle body anda sheet of thermoplastic which comprises: heating and impercrate fibrousreceptacle body to a temperature above the fusion temperature of thethermoplastic sheet to be composited therewith, thereafter shaping andbringing such sheet of thermoplastic into facially contactingconformation with one face of said imperforate heated fibrous body,holding them in contact for a sufficient period of time to permit theheat of the body to fuse the surface strata of the contiguous side ofthe sheet into bonding condition, cooling the opposite side of the sheetto a temperature below the fusion point of the thermoplastic while thesurface strata in contact with the heated fibrous body is being fused,and applying suction to the surface of the fibrous receptacle bodyremote from the thermoplastic sheet during the fusion step of themethod.

6. The method of compositing an imperforate fibrous receptacle body anda sheet of thermoplastic which'comprises: folding a fiat thermoplasticsheet into a shape to conform with one surface of the fibrous receptaclebody with which said sheet is to be thereafter composited, heating thefibrous receptacle body while free from contact with said foldedthermoplastic sheet to a temperature above the fusion temperature ofsaid sheet, thereafter bringing the folded thermoplastic sheet and theheated receptacle body into nesting relation with their contiguous facesin contact, and maintaining them in such contact for a sufficient periodof time to permit the heat of the receptacle body to fuse the surfacestrata of the contiguous sides of the sheet as well as the thermoplasticmaterial of the folds of said sheet into bonding condition whilemaintaining the remote outer surface of the sheet at a temperature belowthe fusion temperature of the thermoplastic sheet, whereby the sheet andfibrous body as well as the contacting surfaces of the folds of thesheet become firmly adhered to- 10 gether by solidification and settingof the resulting thermoplastic bond when subsequently cooled.

7. The method of compositing an imperforate fibrous receptacle body anda sheet of thermoplastic which comprises: heating an imperforate fibrousreceptacle body on a conforming heating die to a temperature above thefusion temperature of the thermoplastic sheet to be composited with saidbody, die forming a flat thermoplastic sheet in dies corresponding inshape and size to the heating die of the receptacle body while allportions of said sheet are maintained below fusion temperature, thennesting the formed thermoplastic sheet and the heated receptacle bodyinto facial contact with one another to cause the heat of the receptaclebody to fuse the contiguous surface strata of the thermoplastic sheetinto bonding condition with the contacting side of the receptacle body.and cooling the opposite surface of the thermoplastic sheet during thefusion step to preclude the fusion of the surface strata thereof, andthereafter permitting the resulting composited assembly to cool for thepurpose of solidifying and setting the resulting thermoplastic bondbetween the thermoplastic sheet and the fibrous receptacle body.

8. The method claimed in claim 7, including the further step of applyingsuction during the fusion step to the surface of the fibrous receptaclebody remote from the thermoplastic sheet.

9. The method of compositing a fibrous body and a sheet of thermoplasticwhich comprises: heating the fibrous body to a temperature above thefusion temperature of the thermoplastic sheet, bringing the thus heatedbody and the thermoplastic sheet into faoially contacting relation andholding them in this relation until the heat of the body fuses thesurface strata of the contacting face of the sheet, and cooling theopposite face of the sheet during the fusion period to contemporaneouslymaintain the surface strata of the latter face of the sheet in solidunfused condition.

10. The method of compositing a fiat layer of fibrous material and asheet of thermoplastic which comprises: heating the layer of fibrousmaterial to a temperature above the fusion temperature of thethermoplastic sheet, bringing the thus heated fibrous layer and thethermoplastic sheet into facial contacting relation and holding them inthis relation until the heat of the layer fuses the surface strata ofthe contacting face of the sheet, and cooling the opposite face of thesheet during the fusion period to contemporaneously maintain the surfacestrata of the latter face of the sheet in solid unfused condition.

SAMUEL S. STEVENS.

REFERENCES CITED The following references are of record in the file ofthis patent:

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